The objective of this project is noninvasive diagnosis of acute pulmonary arterial occulsion in the dog by transmission computed tomography. Ancillary objectives include an analysis of the bronchial blood flow to the occlused segment, an analysis of the efficacy of transmission computed tomography versus chest radiography and radionuclide imaging in the diagnosis of acute pulmonary arterial occulsion, an analysis of the effects of positioning on the appearance of the lesion (as visualized by transmission computed tomography), and study of the effect of lesion age on the computed tomographic findings. During the current grant year, using a state-of-the-art 2-second, 512 x 512 matrix CT scanner, we have been able to establish that decreased density almost invariably develops distal to an acute pulmonary arterial occlusion in the dog. Our goals in the coming year will be to analyze the status of pulmonary and bronchial flow distal to the lesion and to study the effects of positioning and lesion duration upon the computed tomographic appearance of he lung in question.